camshaft shims

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
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camshaft shims

Postby oldandsmelly » Mon Sep 30, 2019 8:43 am

I recently spent a few hours shimming up the end float on the exhaust camshaft. At the start I had about 30 thou of movement and a loud clacking noise which caused onlookers to shake their heads, clearly thinking that my bike was a mechanical disaster waiting to happen.

Shimming up the end float is a tedious job as I took the timing cover on and off about ten times to adjust the end float to a final 2 thou clearance. I then took the bike for a 70 mile ride.

This post isn't a question or a plea for help; rather it's to share the good news in what a big difference such a small job made. There is a noticeable drop in vibration levels at all speeds but it's particularly smoothed the bike out at my normal cruising 50 mph. Also, the horrible clacking rattle has disappeared.

I can now hear the other rattles and rumbles more clearly!

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Re: camshaft shims

Postby cbranni » Mon Sep 30, 2019 8:00 pm

That's a good result Bruce

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Re: camshaft shims

Postby Pharisee » Tue Oct 01, 2019 2:56 pm

As I have my M18S engine on the bench and prompted by this thread, I measured the endfloat on my camshafts using the time honoured method of crushing a small length of fine solder wire between the camshaft and the cover. I appear to have 0.014" - 0.015" endfloat on both camshafts. I can't, however, find a figure quoted anywhere of what the endfloat should be. O'Neill says if it's noisy, put a 0.005" shim in but doesn't give a definitive figure for what it should be. What's considered acceptable?
Also, it only refers to the exhaust camshaft. Should the inlet be shimmed as well?

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Re: camshaft shims

Postby billbeavis » Tue Oct 01, 2019 6:50 pm

My own G3 bottom end was rebuilt years ago by a renowned specialist who still advertises in Jampot. I recall he told me he leaves the shims out when doing these engines. To set end float first both cams are installed then outer cover but no gasket. Then the bushes (the ones in the crankcase) are moved in until end float is eliminated. With the cover then installed with a gasket, end float is set. Bill

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Re: camshaft shims

Postby Pharisee » Tue Oct 01, 2019 8:07 pm

billbeavis wrote:My own G3 bottom end was rebuilt years ago by a renowned specialist who still advertises in Jampot. I recall he told me he leaves the shims out when doing these engines. To set end float first both cams are installed then outer cover but no gasket. Then the bushes (the ones in the crankcase) are moved in until end float is eliminated. With the cover then installed with a gasket, end float is set. Bill


That's what I would have done had the crankcases been split. The bottom end, however, is good and I don't intend to dismantle it, hence the need to shim the camshafts and my request for advice. It would seem, however, that the .002" (thickness of a paper gasket?) that "oldandsmelly" set his to would be about right.

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